U.S. patent number 11,020,289 [Application Number 15/344,239] was granted by the patent office on 2021-06-01 for absorbent structure.
This patent grant is currently assigned to The Procter & Gamble Company. The grantee listed for this patent is The Procter & Gamble Company. Invention is credited to Christopher Philip Bewick-Sonntag, Vito Carla, Jan Claussen, Wade Monroe Hubbard, Jr..
United States Patent |
11,020,289 |
Carla , et al. |
June 1, 2021 |
Absorbent structure
Abstract
An absorbent product comprising a topsheet, a backsheet, and an
absorbent core, the absorbent core comprising an absorbent
structure comprising one or more stratum comprising one or more
enrobeable elements, wherein a smooth transition zone is exhibited
between an acquisition portion of the absorbent structure and a
storage portion of the absorbent structure.
Inventors: |
Carla; Vito (Cincinnati,
OH), Claussen; Jan (Wiesbaden, DE),
Bewick-Sonntag; Christopher Philip (Cincinnati, OH),
Hubbard, Jr.; Wade Monroe (Wyoming, OH) |
Applicant: |
Name |
City |
State |
Country |
Type |
The Procter & Gamble Company |
Cincinnati |
OH |
US |
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Assignee: |
The Procter & Gamble
Company (Cincinnati, OH)
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Family
ID: |
1000005587344 |
Appl.
No.: |
15/344,239 |
Filed: |
November 4, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170119595 A1 |
May 4, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62251049 |
Nov 4, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F
13/53 (20130101); A61F 13/15203 (20130101); A61F
13/534 (20130101); A61F 2013/15373 (20130101); A61F
2013/530839 (20130101); A61F 2013/530905 (20130101); A61F
2013/530817 (20130101) |
Current International
Class: |
A61F
13/53 (20060101); A61F 13/534 (20060101); A61F
13/15 (20060101) |
References Cited
[Referenced By]
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Other References
PCT International Search Report, PCT/US2015/037943, dated Aug. 26,
2015, 9 pages. cited by applicant .
PCT International Search Report, PCT/US2015/029199, dated Jul. 21,
2015, 12 pages. cited by applicant .
PCT International Search Report, PCT/US2015/032154, dated Aug. 26,
2015, 10 pages. cited by applicant .
PCT International Search Report, PCT/US2016/060589, dated Feb. 3,
2017, 13 pages. cited by applicant.
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Primary Examiner: Kidwell; Michele M
Attorney, Agent or Firm: Gallagher; William E.
Claims
What is claimed is:
1. An absorbent product comprising a topsheet, a backsheet, and an
absorbent core, the absorbent core comprising an absorbent
structure comprising a nonwoven acquisition stratum comprising
enrobeable fibers overlying a storage stratum comprising an open
cell HIPE foam, wherein a transition zone is exhibited between the
acquisition stratum and the storage stratum, wherein the transition
zone exhibits a slope that is negative on a plot having the
Position in microns on an X axis wherein the bottom of the
substrate is plotted closest to the origin and top is plotted
furthest away and wherein the NMR signal is on the Y axis when
analyzed using the Kinetics and ID Liquid Distribution by NMR-MOUSE
test protocol, after the second of two 0.5 ml fluid insults over
two 5 minute test periods.
2. The absorbent product of claim 1, wherein the fibers have an
average thickness, as measured per SEM, ca. between 100 and 600
um.
3. The absorbent product of claim 1, wherein the smooth transition
zone comprises pores having an average diameter between 20 micron
and 60 micron.
4. The absorbent product of claim 3, wherein the smooth transition
zone comprises pores having an average diameter between 30 micron
and 40 micron.
5. The absorbent product of claim 1, wherein the smooth transition
zone to caliper ratio is between 0.1 and 0.4.
6. The absorbent product of claim 1, wherein the ratio of the
Capillary Work Potential of the topsheet to the Capillary Work
Potential to the absorbent structure is below 1.4.
7. The absorbent product of claim 3, wherein the ratio of the basis
weight of the fibers to the basis weight of the open-cell foam is
below 0.48.
8. The absorbent product of claim 3, wherein the open-cell foam
comprises an average cell size above 20 micron and a basis weight
above 110 gsm.
9. The absorbent product of claim 1, wherein the smooth transition
zone comprises a heterogeneous mass comprising a portion of the
HIPE foam formed about and enrobing a plurality of the enrobeable
fibers.
10. The absorbent product of claim 1, wherein the nonwoven
acquisition stratum and the storage stratum have been ring-rolled
together.
11. The absorbent product of claim 9 comprising a plurality of
discrete pieces of HIPE foam each formed about and enrobing a
plurality of the enrobeable fibers.
Description
FIELD OF THE INVENTION
The present invention relates to absorbent structures useful in
absorbent articles such as diapers, incontinent briefs, training
pants, diaper holders and liners, sanitary hygiene garments, and
the like. Specifically, the present invention relates to an
absorbent structure that have a smooth transition zone within the
absorbent structure and a fibrous network.
BACKGROUND OF THE INVENTION
Many types of materials have been used in absorbent cores for
absorbent articles including but not limited to cellulose,
superabsorbent particles, foams, and fibrous substrates. Different
stratum having potentially more than one layer are often combined
to create an absorbent core. For example, a stratum may be designed
for better acquisition while another stratum may be designed for
storage. The two stratum are then combined by placing one in
contact with the other to create an absorbent core.
Ultimately, in regards to an absorbent core, an acquisition layer
is placed onto a storage layer to create the absorbent core. This
may occur within a single stratum or using multiple stratum. This
occurs with all the different core materials contemplated including
the placement of one emulsion onto another emulsion prior to
polymerization. When the layers or stratum are placed in contact,
there is an understanding that fluid will eventually travel to the
desired storage portion of the core. However, the interface between
the acquisition and storage sections is neither designed nor
optimized.
Within an absorbent core, the material structure is ultimately
responsible for both driving force (capillary suction) and
resistance to flow (inverse of through-plane permeability) in such
a way that whenever the structure presents high surface/volume
ratios the capillary suction increases (because more surfaces are
available to sustain capillary forces) but the permeability
decreases, because the flow becomes more tortuous. Conversely,
whenever the ratio surface to volume is low in a porous material,
then the resistance to flow is reduced (high permeability) at the
expenses of the capillary suction.
Regardless of the actual nature of the capillary pressure curves
for each individual layer comprising an absorbent structure used as
diaper or hygienic pad, both industrial experience and flow through
porous media theory show that the interface between the individual
layer represents a significant barrier to fluid movement. This has
to do with the presence of a discontinuity in the path of the
moving fluid which does not `like to jump` across layers. This
ultimately results in residual moisture in the proximity of the
surface/body interface which would negatively impact the consumer
dryness feeling and perception.
Therefore there exists a need to create an absorbent core
comprising a single stratum wherein the transition from acquisition
to storage is optimized to increase the overall absorbent core
efficiency. Additionally, there exists a need to characterize the
transition. Lastly, there exists a need to integrate an absorbent
core with an optimized acquisition to storage stratum into an
absorbent article where the absorbent core is optimized to work
with the topsheet so that the consumer has an improved
experience.
SUMMARY OF THE INVENTION
An absorbent product comprising a topsheet, a backsheet, and an
absorbent core is disclosed. The absorbent core comprising an
absorbent structure comprising one or more stratum comprising one
or more enrobeable elements, wherein a smooth transition zone is
exhibited between an acquisition portion of the absorbent structure
and a storage portion of the absorbent structure.
An absorbent product comprising a topsheet, a backsheet, and an
absorbent core is further disclosed. The absorbent core comprising
an absorbent structure comprising one or more stratum comprising
one or more enrobeable elements and open cell foam, wherein a
smooth transition zone is exhibited between an acquisition portion
of the absorbent structure and a storage portion of the absorbent
structure, wherein the smooth transition zone is demonstrated by a
negative slope by a NMR technique.
An absorbent product comprising a topsheet, a backsheet, and an
absorbent core is further disclosed. The absorbent core comprising
an absorbent structure comprising one or more stratum comprising
one or more enrobeable elements and open cell foam, wherein a
smooth transition zone is exhibited between an acquisition portion
of the absorbent structure and a storage portion of the absorbent
structure, wherein the smooth transition zone is demonstrated by a
negative slope by a NMR technique, wherein the smooth transition
zone comprises of pores of average diameter between 20 micron and
60 micron.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing
out and distinctly claiming the subject matter of the present
invention, it is believed that the invention can be more readily
understood from the following description taken in connection with
the accompanying drawings, in which:
FIG. 1 is an SEM micrograph of a heterogeneous mass.
FIG. 2 shows a plot of an NMR profile.
FIG. 3 shows a plot of an NMR profile.
FIGS. 4A-B shows a plot of an NMR profile.
FIG. 5 shows a kinetic plot of an NMR profile.
FIG. 6 shows a portion of a NMR sensor.
FIG. 7 shows a portion of a NMR sensor.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the term "bicomponent fibers" refers to fibers
which have been formed from at least two different polymers
extruded from separate extruders but spun together to form one
fiber. Bicomponent fibers are also sometimes referred to as
conjugate fibers or multicomponent fibers. The polymers are
arranged in substantially constantly positioned distinct zones
across the cross-section of the bicomponent fibers and extend
continuously along the length of the bicomponent fibers. The
configuration of such a bicomponent fiber may be, for example, a
sheath/core arrangement wherein one polymer is surrounded by
another, or may be a side-by-side arrangement, a pie arrangement,
or an "islands-in-the-sea" arrangement.
As used herein, the term "biconstituent fibers" refers to fibers
which have been formed from at least two polymers extruded from the
same extruder as a blend. Biconstituent fibers do not have the
various polymer components arranged in relatively constantly
positioned distinct zones across the cross-sectional area of the
fiber and the various polymers are usually not continuous along the
entire length of the fiber, instead usually forming fibrils which
start and end at random. Biconstituent fibers are sometimes also
referred to as multiconstituent fibers.
In the following description the term "cellulose fibers" is used.
Cellulose fibers comprise naturally occurring fibers based on
cellulose, such as, for example cotton, linen, etc. Wood pulp
fibers are one example of cellulose fibers according to the present
invention. Man-made fibers derived from cellulose, such as
regenerated cellulose, e.g. viscose or partially or fully
acetylated cellulose derivatives (e.g. cellulose acetate or
triacetate), are also considered as cellulose fibers according to
the present invention.
The term "disposable" is used herein to describe articles, which
are not intended to be laundered or otherwise restored or reused as
an article (i.e. they are intended to be discarded after a single
use and possibly to be recycled, composted or otherwise disposed of
in an environmentally compatible manner). The absorbent article
comprising an absorbent structure according to the present
invention can be for example a sanitary napkin, a panty liner, an
adult incontinence product, a diaper, or any other product designed
to absorb a bodily exudate. The absorbent structure of the present
invention will be herein described in the context of a typical
absorbent article, such as, for example, a sanitary napkin.
Typically, such articles may comprise a liquid pervious topsheet, a
backsheet and an absorbent core intermediate the topsheet and the
backsheet.
As used herein, an "enrobeable element" refers to an element that
may be enrobed by the foam. The enrobeable element may be, for
example, a fiber, a group of fibers, a tuft, or a section of a film
between two apertures. It is understood that other elements are
contemplated by the present invention.
A "fiber" as used herein, refers to any material that may be part
of a fibrous structure. Fibers may be natural or synthetic. Fibers
may be absorbent or non-absorbent.
A "fibrous structure" as used herein, refers to materials which may
be broken into one or more fibers. A fibrous structure can be
absorbent or adsorbent. A fibrous structure may exhibit capillary
action as well as porosity and permeability.
As used herein, the term "immobilize" refers to the reduction or
the elimination of movement or motion.
As used herein, the term "meltblowing" refers to a process in which
fibers are formed by extruding a molten thermoplastic material
through a plurality of fine, usually circular, die capillaries as
molten threads or filaments into converging high velocity, usually
heated, gas (for example air) streams which attenuate the filaments
of molten thermoplastic material to reduce their diameter.
Thereafter, the meltblown fibers are carried by the high velocity
gas stream and are deposited on a collecting surface, often while
still tacky, to form a web of randomly dispersed meltblown
fibers.
As used herein, the term "monocomponent" fiber refers to a fiber
formed from one or more extruders using only one polymer. This is
not meant to exclude fibers formed from one polymer to which small
amounts of additives have been added for coloration, antistatic
properties, lubrication, hydrophilicity, etc. These additives, for
example titanium dioxide for coloration, are generally present in
an amount less than about 5 weight percent and more typically about
2 weight percent.
As used herein, the term "non-round fibers" describes fibers having
a non-round cross-section, and includes "shaped fibers" and
"capillary channel fibers." Such fibers may be solid or hollow, and
they may be tri-lobal, delta-shaped, and may be fibers having
capillary channels on their outer surfaces. The capillary channels
may be of various cross-sectional shapes such as "U-shaped",
"H-shaped", "C-shaped" and "V-shaped". One practical capillary
channel fiber is T-401, designated as 4DG fiber available from
Fiber Innovation Technologies, Johnson City, Tenn. T-401 fiber is a
polyethylene terephthalate (PET polyester).
As used herein, the term "nonwoven web" refers to a web having a
structure of individual fibers or threads which are interlaid, but
not in a repeating pattern as in a woven or knitted fabric, which
do not typically have randomly oriented fibers. Nonwoven webs or
fabrics have been formed from many processes, such as, for example,
electro-spinning, meltblowing processes, spunbonding processes,
spunlacing processes, hydroentangling, airlaying, and bonded carded
web processes, including carded thermal bonding. The basis weight
of nonwoven fabrics is usually expressed in grams per square meter
(gsm). The basis weight of the laminate web is the combined basis
weight of the constituent layers and any other added components.
Fiber diameters are usually expressed in microns; fiber size may
also be expressed in denier, which is a unit of weight per length
of fiber. The basis weight of laminate webs suitable for use in an
article of the present invention may range from about 10 gsm to
about 100 gsm, depending on the ultimate use of the web.
As used herein, the term "polymer" generally includes, but is not
limited to, homopolymers, copolymers, such as for example, block,
graft, random and alternating copolymers, terpolymers, etc., and
blends and modifications thereof. In addition, unless otherwise
specifically limited, the term "polymer" includes all possible
geometric configurations of the material. The configurations
include, but are not limited to, isotactic, atactic, syndiotactic,
and random symmetries.
As used herein, the term "recovery energy" relates to an indicator
of how well an absorbent structure or absorbent product may retain
or regain is original shape. More specifically, "recovery energy"
is a measure of the amount of work the absorbent structure or the
absorbent product will perform against the consumer's body and/or
garment following compression. Without being bound by theory, the
upper limit for recovery energy should be the compressive energy
i.e. a fully recovered product when removed from the consumer's
body/garment. Dry recovery energy for between 1 and 20 cycles
should be less than 250% the dry compressive energy of a new
product.
As used herein, a "smooth transition zone" (STZ) refers to a
transition zone between a portion of an absorbent structure
designed for acquisition and a portion of an absorbent structure
designed for storage that exhibits a slope that is negative on a
plot having the Position in microns on an X axis wherein the bottom
of the substrate is plotted closest to the origin and top is
plotted furthest away and wherein the NMR signal is on the Y axis
when analyzed using the Kinetics and 1D Liquid Distribution by
NMR-MOUSE test protocol, after the second of two 0.5 ml fluid
insults over two 5 minute test periods. The inventors have
determined that an ideal acquisition and storage stratum will have
a ratio of fluid stored in the acquisition layer to fluid stored in
the storage layer of the stratum of greater than 1.5 to 1, greater
than 2 to 1, greater than 2.5 to 1, or greater than 3 to 1 after
the first and second 0.5 ml gushes.
As used herein, an "integrated topsheet/secondary topsheet zone"
refers to a transition zone between a fibrous topsheet and a
fibrous secondary topsheet that exhibits a slope that is negative
on a plot having the Position in microns on an X axis wherein the
bottom of the substrate is plotted closest to the origin and top is
plotted furthest away and wherein the NMR signal is on the Y axis
when analyzed using the Kinetics and 1D Liquid Distribution by
NMR-MOUSE test protocol, after the second of two 0.5 ml fluid
insults over two 5 minute test periods. The inventors have
determined that an ideal topsheet and absorbent structure
combination will leave a ratio of fluid retained in the topsheet to
fluid stored in the absorbent structure of less than 1 to 10, less
than 1 to 15, less than 1 to 20, less than 1 to 25, or less than 1
to 30.
As used herein, "spunbond fibers" refers to small diameter fibers
which are formed by extruding molten thermoplastic material as
filaments from a plurality of fine, usually circular capillaries of
a spinneret with the diameter of the extruded filaments then being
rapidly reduced. Spunbond fibers are generally not tacky when they
are deposited on a collecting surface. Spunbond fibers are
generally continuous and have average diameters (from a sample size
of at least 10 fibers) larger than 7 microns, and more
particularly, between about 10 and 40 microns.
As used herein, a "strata" or "stratum" relates to one or more
layers combined to create a single stratum which may be combined
with other stratum to form an absorbent core. As used herein, a
"tuft" or chad relates to discrete integral extensions of the
fibers of a nonwoven web. Each tuft may comprise a plurality of
looped, aligned fibers extending outwardly from the surface of the
web. Each tuft may comprise a plurality of non-looped fibers that
extend outwardly from the surface of the web. Each tuft may
comprise a plurality of fibers which are integral extensions of the
fibers of two or more integrated nonwoven webs.
As used herein, a "usage cycle" relates to the duration of use of
the absorbent structure as it transitions from a dry state to a
saturated wet state.
While particular embodiments of the present invention have been
illustrated and described, it would be obvious to those skilled in
the art that various other changes and modifications may be made
without departing from the spirit and scope of the invention.
GENERAL SUMMARY
The present invention relates to an absorbent structure that
contains a stratum comprising a fibrous network having a smooth
transition zone between acquisition portion and storage portion of
the absorbent core. The smooth transition zone is demonstrated
using LF-NMR (Low Field Nuclear Magnetic Resonance) as a
methodology to characterize fluid partitioning inside complex
porous media structure to show the existence of a smooth transition
zone and to show the advantage created by the smooth transition
zone. A single stratum may comprise one or more absorbent layers.
One or more absorbent core stratums may be a heterogeneous mass
comprising enrobeable elements and open cell foam, a cellulose
layer, a layer comprising a substrate, a superabsorbent, and an
adhesive layer, a layer comprising airfelt fibers, and a layer of
foam.
A stratum may be a heterogeneous mass comprising one or more
enrobeable elements and one or more discrete open cell foam pieces.
The heterogeneous mass has a depth, a width, and a height. The
absorbent structure may be used as any part of an absorbent article
including, for example, a part of an absorbent core, as an
absorbent core, and/or as a topsheet for absorbent articles such as
sanitary napkins, panty liners, tampons, interlabial devices, wound
dressings, diapers, adult incontinence articles, and the like,
which are intended for the absorption of body fluids, such as
menses or blood or vaginal discharges or urine. The absorbent
structure may be used in any product utilized to absorb and retain
a fluid including surface wipes. The absorbent structure may be
used as a paper towel. Exemplary absorbent articles in the context
of the present invention are disposable absorbent articles.
The absorbent structure single stratum may comprise a heterogeneous
mass layer as those described in U.S. patent application No.
61/988,565, filed May 5, 2014; U.S. patent application No.
62/115,921, filed Feb. 13, 2015; or U.S. patent application No.
62/018,212. The heterogeneous mass layer has a depth, a width, and
a height.
The absorbent structures single stratum may be a heterogeneous mass
comprising enrobeable elements and one or more portions of foam
pieces. The discrete portions of foam pieces are open-celled foam.
The foam may be a High Internal Phase Emulsion (HIPE) foam.
The absorbent structure single stratum may be an absorbent core for
an absorbent article wherein the absorbent core comprises a
heterogeneous mass comprising fibers and one or more discrete
portions of foam that are immobilized in the heterogeneous mass or
may be combined with other layers to form an absorbent core.
In the following description of the invention, the surface of the
article, or of each component thereof, which in use faces in the
direction of the wearer is called wearer-facing surface.
Conversely, the surface facing in use in the direction of the
garment is called garment-facing surface. The absorbent article of
the present invention, as well as any element thereof, such as, for
example the absorbent core, has therefore a wearer-facing surface
and a garment-facing surface.
The present invention relates to an absorbent structure single
stratum that contains one or more discrete open-cell foam pieces
foams that are integrated into a heterogeneous mass comprising one
or more enrobeable elements integrated into the one or more
open-cell foams such that the two may be intertwined.
The open-cell foam pieces may comprise between 1% of the
heterogeneous mass by volume to 99% of the heterogeneous mass by
volume, such as, for example, 5% by volume, 10% by volume, 15% by
volume, 20% by volume, 25% by volume, 30% by volume, 35% by volume,
40% by volume, 45% by volume, 50% by volume, 55% by volume, 60% by
volume, 65% by volume, 70% by volume, 75% by volume, 80% by volume,
85% by volume, 90% by volume, or 95% by volume.
The heterogeneous mass may have void space found between the
enrobeable elements, between the enrobeable elements and the
enrobed elements, and between enrobed elements. The void space may
contain a gas such as air. The void space may represent between 1%
and 95% of the total volume for a fixed amount of volume of the
heterogeneous mass, such as, for example, 5%, 10%, 15%, 20%, 25%,
30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% of
the total volume for a fixed amount of volume of the heterogeneous
mass.
The combination of open-cell foam pieces and void space within the
heterogeneous mass may exhibit an absorbency of between 10 g/g to
200 g/g of the, such as for example, between 20 g/g and 190 g/g of
the heterogeneous mass, such as, for example 30 g/g, 40 g/g, 60
g/g, 80 g/g, 100 g/g, 120 g/g, 140 g/g 160 g/g 180 g/g or 190 g/g
of the heterogeneous mass. Absorbency may be quantified according
to the EDANA Nonwoven Absorption method 10.4-02.
The open-cell foam pieces are discrete foam pieces intertwined
within and throughout a heterogeneous mass such that the open-cell
foam enrobes one or more of the enrobeable elements such as, for
example, fibers within the mass. The open-cell foam may be
polymerized around the enrobeable elements.
A discrete open-cell foam piece may enrobe more than one enrobeable
element. The enrobeable elements may be enrobed together as a
bunch. Alternatively, more than one enrobeable element may be
enrobed by the discrete open-cell foam piece without contacting
another enrobeable element.
A discrete open-cell foam piece may be immobilized such that the
discrete open-cell foam piece does not change location within the
heterogeneous mass during use of the absorbent structure.
A plurality of discrete open-cell foams may be immobilized such
that the discrete open-cell foam pieces do not change location
within the heterogeneous mass during use of the absorbent
structure.
One or more discrete foam pieces may be immobilized within the
heterogeneous mass such that the one or more discrete foam pieces
do not change location after being spun at 300 rotations per minute
for 30 seconds.
The open-cell foam pieces may be discrete. Open-cell foam pieces
are considered discrete in that they are not continuous throughout
the entire heterogeneous mass. Not continuous throughout the entire
heterogeneous mass represents that at any given point in the
heterogeneous mass, the open-cell absorbent foam is not continuous
in at least one of the cross sections of a longitudinal, a
vertical, and a lateral plane of the heterogeneous mass. The
absorbent foam may or may not be continuous in the lateral and the
vertical planes of the cross section for a given point in the
heterogeneous mass. The absorbent foam may or may not be continuous
in the longitudinal and the vertical planes of the cross section
for a given point in the heterogeneous mass. The absorbent foam may
or may not be continuous in the longitudinal and the lateral planes
of the cross section for a given point in the heterogeneous
mass.
When the open-cell foam is not continuous in at least one of the
cross sections of the longitudinal, the vertical, and the lateral
plane of the heterogeneous mass, one or both of either the
enrobeable elements or the open-cell foam pieces may be
bi-continuous throughout the heterogeneous mass.
The open-cell foam pieces may be located at any point in the
heterogeneous mass. A foam piece may be surrounded by the elements
that make up the enrobeable elements. A foam piece may be located
on the outer perimeter of the heterogeneous mass such that only a
portion of the foam piece is entangled with the elements of the
heterogeneous mass.
The open-cell foam pieces may expand upon being contacted by a
fluid to form a channel of discrete open-cell foam pieces. The
open-cell foam pieces may or may not be in contact prior to being
expanded by a fluid.
An open-celled foam may be integrated onto the enrobeable elements
prior to being polymerized. The open-cell foam pieces may be
partially polymerized prior to being impregnated into or onto the
enrobeable elements such that they become intertwined. After being
impregnated into or onto the enrobeable elements, the open-celled
foam in either a liquid or solid state are polymerized to form one
or more open-cell foam pieces. The open-celled foam may be
polymerized using any known method including, for example, heat,
UV, and infrared. Following the polymerization of a water in oil
open-cell foam emulsion, the resulting open-cell foam is saturated
with aqueous phase that needs to be removed to obtain a
substantially dry open-cell foam. Removal of the saturated aqueous
phase or dewatering may occur using nip rollers, and vacuum.
Utilizing a nip roller may also reduce the thickness of the
heterogeneous mass such that the heterogeneous mass will remain
thin until the open-cell foam pieces entwined in the heterogeneous
mass are exposed to fluid.
Dependent upon the desired foam density, polymer composition,
specific surface area, or pore-size (also referred to as cell
size), the open-celled foam may be made with different chemical
composition, physical properties, or both. For instance, dependent
upon the chemical composition, an open-celled foam may have a
density of 0.0010 g/cc to about 0.25 g/cc, or from 0.002 g/cc to
about 0.2 g/cc, or from about 0.005 g/cc to about 0.15 g/cc, or
from about 0.01 g/cc to about 0.1 g/cc, or from about 0.02 g/cc to
about 0.08 g/cc, or about 0.04 g/cc.
Open-cell foam pore-sizes may range in average diameter of from 1
to 800 such as, for example, between 50 and 700 between 100 and 600
between 200 and 500 between 300 and 400 .mu.m.
The foam pieces may have a relatively uniform cell size. For
example, the average cell size on one major surface may be about
the same or vary by no greater than 10% as compared to the opposing
major surface. The average cell size of one major surface of the
foam may differ from the opposing surface. For example, in the
foaming of a thermosetting material it is not uncommon for a
portion of the cells at the bottom of the cell structure to
collapse resulting in a lower average cell size on one surface. The
cell size may be determined based upon the method found below.
The foams produced from the present invention are relatively
open-celled. This refers to the individual cells or pores of the
foam being in substantially unobstructed communication with
adjoining cells. The cells in such substantially open-celled foam
structures have intercellular openings or windows that are large
enough to permit ready fluid transfer from one cell to another
within the foam structure. For purpose of the present invention, a
foam is considered "open-celled" if at least about 80% of the cells
in the foam that are at least 1 .mu.m in average diameter size are
in fluid communication with at least one adjoining cell.
In addition to being open-celled, the foams may be sufficiently
hydrophilic to permit the foam to absorb aqueous fluids, for
example the internal surfaces of a foam may be rendered hydrophilic
by residual hydrophilizing surfactants or salts left in the foam
following polymerization, by selected post-polymerization foam
treatment procedures (as described hereafter), or combinations of
both.
For example when used in certain absorbent articles, an open-cell
foam may be flexible and exhibit an appropriate glass transition
temperature (Tg). The Tg represents the midpoint of the transition
between the glassy and rubbery states of the polymer.
The Tg of a region may be less than about 200.degree. C. for foams
used at about ambient temperature conditions, or less than about
90.degree. C. The Tg may be less than 50.degree. C.
The open-cell foam pieces may be distributed in any suitable manner
throughout the heterogeneous mass. The open-cell foam pieces may be
profiled along the vertical axis such that smaller pieces are
located above larger pieces. Alternatively, the pieces may be
profiled such that smaller pieces are below larger pieces. The
open-cell pieces may be profiled along a vertical axis such that
they alternate in size along the axis.
The open-cell foam pieces may be profiled along the longitudinal
axis such that smaller pieces are located in front of larger
pieces. Alternatively, the pieces may be profiled such that smaller
pieces are behind larger pieces. The open-cell pieces may be
profiled along a longitudinal axis such that they alternate in size
along the axis.
The open-cell foam pieces may be profiled along the lateral axis
such the size of the pieces goes from small to large or from large
to small along the lateral axis. Alternatively, the open-cell
pieces may be profiled along a lateral axis such that they
alternate in size along the axis.
The open-cell foam pieces may be profiled along any one of the
longitudinal, lateral, or vertical axis based on one or more
characteristics of the open-cell foam pieces. Characteristics by
which the open-cell foam pieces may be profiled within the
heterogeneous mass may include, for example, absorbency, density,
cell size, and combinations thereof.
The open-cell foam pieces may be profiled along any one of the
longitudinal, lateral, or vertical axis based on the composition of
the open-cell foam. The open-cell foam pieces may have one
composition exhibiting desirable characteristics in the front of
the heterogeneous mass and a different composition in the back of
the heterogeneous mass designed to exhibit different
characteristics. The profiling of the open-cell foam pieces may be
either symmetric or asymmetric about any of the prior mentioned
axes or orientations.
The open-cell foam pieces may be distributed along the longitudinal
and lateral axis of the heterogeneous mass in any suitable form.
The open-cell foam pieces may be distributed in a manner that forms
a design or shape when viewed from a top planar view. The open-cell
foam pieces may be distributed in a manner that forms stripes,
ellipticals, squares, or any other known shape or pattern.
The distribution may be optimized dependent on the intended use of
the heterogeneous mass. For example, a different distribution may
be chosen for the absorption of aqueous fluids such as urine when
used in a diaper or water when used in a paper towel versus for the
absorption of a proteinaceous fluid such as menses. Further, the
distribution may be optimized for uses such as dosing an active or
to use the foam as a reinforcing element.
Different types of foams may be used in one heterogeneous mass. For
example, some of the foam pieces may be polymerized HIPE while
other pieces may be made from polyurethane. The pieces may be
located at specific locations within the mass based on their
properties to optimize the performance of the heterogeneous
mass.
The foam pieces may be similar in composition yet exhibit different
properties. For example, using HIPE foam, some foam pieces may be
thin until wet while others may have been expanded within the
heterogeneous mass.
The foam pieces and enrobeable elements may be selected to
complement each other. For example, a foam that exhibits high
permeability with low capillarity may enrobe an element that
exhibits high capillarity to wick the fluid through the
heterogeneous mass. It is understood that other combinations may be
possible wherein the foam pieces complement each other or wherein
the foam pieces and enrobeable elements both exhibit similar
properties.
Profiling may occur using more than one heterogeneous mass with
each heterogeneous mass having one or more types of foam pieces.
The plurality of heterogeneous masses may be layered so that the
foam is profiled along any one of the longitudinal, lateral, or
vertical axis based on one or more characteristics of the open-cell
foam pieces for an overall product that contains the plurality of
heterogeneous masses. Further, each heterogeneous mass may have a
different enrobeable element to which the foam is attached. For
example, a first heterogeneous mass may have foam particles
enrobing a nonwoven while a second heterogeneous mass adjacent the
first heterogeneous mass may have foam particles enrobing a film or
one surface of a film.
The open-celled foam may be a thermoset polymeric foam made from
the polymerization of a High Internal Phase Emulsion (HIPE), also
referred to as a polyHIPE. To form a HIPE, an aqueous phase and an
oil phase are combined in a ratio between about 8:1 and 140:1. The
aqueous phase to oil phase ratio may be between about 10:1 and
about 75:1, and the aqueous phase to oil phase ratio may be between
about 13:1 and about 65:1. This is termed the "water-to-oil" or W:O
ratio and may be used to determine the density of the resulting
polyHIPE foam. As discussed, the oil phase may contain one or more
of monomers, comonomers, photoinitiators, crosslinkers, and
emulsifiers, as well as optional components. The water phase may
contain water and one or more components such as electrolyte,
initiator, or optional components.
The open-cell foam may be formed from the combined aqueous and oil
phases by subjecting these combined phases to shear agitation in a
mixing chamber or mixing zone. The combined aqueous and oil phases
are subjected to shear agitation to produce a stable HIPE having
aqueous droplets of the desired size. An initiator may be present
in the aqueous phase, or an initiator may be introduced during the
foam making process, or after the HIPE has been formed. The
emulsion making process produces a HIPE where the aqueous phase
droplets are dispersed to such an extent that the resulting HIPE
foam will have the desired structural characteristics.
Emulsification of the aqueous and oil phase combination in the
mixing zone may involve the use of a mixing or agitation device
such as an impeller, by passing the combined aqueous and oil phases
through a series of static mixers at a rate necessary to impart the
requisite shear, or combinations of both. Once formed, the HIPE may
then be withdrawn or pumped from the mixing zone. One method for
forming HIPEs using a continuous process is described in U.S. Pat.
No. 5,149,720 (DesMarais et al), issued Sep. 22, 1992; U.S. Pat.
No. 5,827,909 (DesMarais) issued Oct. 27, 1998; and U.S. Pat. No.
6,369,121 (Catalfamo et al.) issued Apr. 9, 2002.
The emulsion may be withdrawn or pumped from the mixing zone and
impregnated into or onto a mass prior to being fully polymerized.
Once fully polymerized, the foam pieces and the elements are
intertwined such that discrete foam pieces are bisected by the
elements comprising the mass and such that parts of discrete foam
pieces enrobe portions of one or more of the elements comprising
the heterogeneous mass.
Following polymerization, the resulting foam pieces are saturated
with aqueous phase that needs to be removed to obtain substantially
dry foam pieces. Foam pieces may be squeezed free of most of the
aqueous phase by using compression, for example by running the
heterogeneous mass comprising the foam pieces through one or more
pairs of nip rollers. The nip rollers may be positioned such that
they squeeze the aqueous phase out of the foam pieces. The nip
rollers may be porous and have a vacuum applied from the inside
such that they assist in drawing aqueous phase out of the foam
pieces. Nip rollers may be positioned in pairs, such that a first
nip roller is located above a liquid permeable belt, such as a belt
having pores or composed of a mesh-like material and a second
opposing nip roller facing the first nip roller and located below
the liquid permeable belt. One of the pair, for example the first
nip roller may be pressurized while the other, for example the
second nip roller, may be evacuated, so as to both blow and draw
the aqueous phase out the of the foam. The nip rollers may also be
heated to assist in removing the aqueous phase. Nip rollers may be
applied to non-rigid foams, that is, foams whose walls would not be
destroyed by compressing the foam pieces.
In place of or in combination with nip rollers, the aqueous phase
may be removed by sending the foam pieces through a drying zone
where it is heated, exposed to a vacuum, or a combination of heat
and vacuum exposure. Heat may be applied, for example, by running
the foam though a forced air oven, IR oven, microwave oven or
radiowave oven. The extent to which a foam is dried depends on the
application. Greater than 50% of the aqueous phase may be removed.
Greater than 90%, and in still other embodiments greater than 95%
of the aqueous phase may be removed during the drying process.
Open-cell foam may be produced from the polymerization of the
monomers having a continuous oil phase of a High Internal Phase
Emulsion (HIPE). The HIPE may have two phases. One phase is a
continuous oil phase having monomers that are polymerized to form a
HIPE foam and an emulsifier to help stabilize the HIPE. The oil
phase may also include one or more photoinitiators. The monomer
component may be present in an amount of from about 80% to about
99%, and in certain embodiments from about 85% to about 95% by
weight of the oil phase. The emulsifier component, which is soluble
in the oil phase and suitable for forming a stable water-in-oil
emulsion may be present in the oil phase in an amount of from about
1% to about 20% by weight of the oil phase. The emulsion may be
formed at an emulsification temperature of from about 10.degree. C.
to about 130.degree. C. and in certain embodiments from about
50.degree. C. to about 100.degree. C.
In general, the monomers will include from about 20% to about 97%
by weight of the oil phase at least one substantially
water-insoluble monofunctional alkyl acrylate or alkyl
methacrylate. For example, monomers of this type may include
C.sub.4-C.sub.18 alkyl acrylates and C.sub.2-C.sub.18
methacrylates, such as ethylhexyl acrylate, butyl acrylate, hexyl
acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, isodecyl
acrylate, tetradecyl acrylate, benzyl acrylate, nonyl phenyl
acrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl
methacrylate, nonyl methacrylate, decyl methacrylate, isodecyl
methacrylate, dodecyl methacrylate, tetradecyl methacrylate, and
octadecyl methacrylate.
The oil phase may also have from about 2% to about 40%, and in
certain embodiments from about 10% to about 30%, by weight of the
oil phase, a substantially water-insoluble, polyfunctional
crosslinking alkyl acrylate or methacrylate. This crosslinking
comonomer, or crosslinker, is added to confer strength and
resilience to the resulting HIPE foam. Examples of crosslinking
monomers of this type may have monomers containing two or more
activated acrylate, methacrylate groups, or combinations thereof.
Nonlimiting examples of this group include
1,6-hexanedioldiacrylate, 1,4-butanedioldimethacrylate,
trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,
1,12-dodecyldimethacrylate, 1,14-tetradecanedioldimethacrylate,
ethylene glycol dimethacrylate, neopentyl glycol diacrylate
(2,2-dimethylpropanediol diacrylate), hexanediol acrylate
methacrylate, glucose pentaacrylate, sorbitan pentaacrylate, and
the like. Other examples of crosslinkers contain a mixture of
acrylate and methacrylate moieties, such as ethylene glycol
acrylate-methacrylate and neopentyl glycol acrylate-methacrylate.
The ratio of methacrylate:acrylate group in the mixed crosslinker
may be varied from 50:50 to any other ratio as needed.
Any third substantially water-insoluble comonomer may be added to
the oil phase in weight percentages of from about 0% to about 15%
by weight of the oil phase, in certain embodiments from about 2% to
about 8%, to modify properties of the HIPE foams. "Toughening"
monomers may be desired which impart toughness to the resulting
HIPE foam. These include monomers such as styrene, vinyl chloride,
vinylidene chloride, isoprene, and chloroprene. Without being bound
by theory, it is believed that such monomers aid in stabilizing the
HIPE during polymerization (also known as "curing") to provide a
more homogeneous and better formed HIPE foam which results in
better toughness, tensile strength, abrasion resistance, and the
like. Monomers may also be added to confer flame retardancy as
disclosed in U.S. Pat. No. 6,160,028 (Dyer) issued Dec. 12, 2000.
Monomers may be added to confer color, for example vinyl ferrocene,
fluorescent properties, radiation resistance, opacity to radiation,
for example lead tetraacrylate, to disperse charge, to reflect
incident infrared light, to absorb radio waves, to form a wettable
surface on the HIPE foam struts, or for any other desired property
in a HIPE foam. In some cases, these additional monomers may slow
the overall process of conversion of HIPE to HIPE foam, the
tradeoff being necessary if the desired property is to be
conferred. Thus, such monomers may be used to slow down the
polymerization rate of a HIPE. Examples of monomers of this type
may have styrene and vinyl chloride.
The oil phase may further contain an emulsifier used for
stabilizing the HIPE. Emulsifiers used in a HIPE may include: (a)
sorbitan monoesters of branched C.sub.16-C.sub.24 fatty acids;
linear unsaturated C.sub.16-C.sub.22 fatty acids; and linear
saturated C.sub.12-C.sub.14 fatty acids, such as sorbitan
monooleate, sorbitan monomyristate, and sorbitan monoesters,
sorbitan monolaurate diglycerol monooleate (DGMO), polyglycerol
monoisostearate (PGMIS), and polyglycerol monomyristate (PGMM); (b)
polyglycerol monoesters of -branched C.sub.16-C.sub.24 fatty acids,
linear unsaturated C.sub.16-C.sub.22 fatty acids, or linear
saturated C.sub.12-C.sub.14 fatty acids, such as diglycerol
monooleate (for example diglycerol monoesters of C18:1 fatty
acids), diglycerol monomyristate, diglycerol monoisostearate, and
diglycerol monoesters; (c) diglycerol monoaliphatic ethers of
-branched C.sub.16-C.sub.24 alcohols, linear unsaturated
C.sub.16-C.sub.22 alcohols, and linear saturated C.sub.12-C.sub.14
alcohols, and mixtures of these emulsifiers. See U.S. Pat. No.
5,287,207 (Dyer et al.), issued Feb. 7, 1995 and U.S. Pat. No.
5,500,451 (Goldman et al.) issued Mar. 19, 1996. Another emulsifier
that may be used is polyglycerol succinate (PGS), which is formed
from an alkyl succinate, glycerol, and triglycerol.
Such emulsifiers, and combinations thereof, may be added to the oil
phase so that they may have between about 1% and about 20%, in
certain embodiments from about 2% to about 15%, and in certain
other embodiments from about 3% to about 12% by weight of the oil
phase. Coemulsifiers may also be used to provide additional control
of cell size, cell size distribution, and emulsion stability,
particularly at higher temperatures, for example greater than about
65.degree. C. Examples of coemulsifiers include phosphatidyl
cholines and phosphatidyl choline-containing compositions,
aliphatic betaines, long chain C.sub.12-C.sub.22 dialiphatic
quaternary ammonium salts, short chain C.sub.1-C.sub.4 dialiphatic
quaternary ammonium salts, long chain C.sub.12-C.sub.22
dialkoyl(alkenoyl)-2-hydroxyethyl, short chain C.sub.1-C.sub.4
dialiphatic quaternary ammonium salts, long chain C.sub.12-C.sub.22
dialiphatic imidazolinium quaternary ammonium salts, short chain
C.sub.1-C.sub.4 dialiphatic imidazolinium quaternary ammonium
salts, long chain C.sub.12-C.sub.22 monoaliphatic benzyl quaternary
ammonium salts, long chain C.sub.12-C.sub.22
dialkoyl(alkenoyl)-2-aminoethyl, short chain C.sub.1-C.sub.4
monoaliphatic benzyl quaternary ammonium salts, short chain
C.sub.1-C.sub.4 monohydroxyaliphatic quaternary ammonium salts.
Ditallow dimethyl ammonium methyl sulfate (DTDMAMS) may be used as
a coemulsifier.
The oil phase may comprise a photoinitiator at between about 0.05%
and about 10%, and in certain embodiments between about 0.2% and
about 10% by weight of the oil phase. Lower amounts of
photoinitiator allow light to better penetrate the HIPE foam, which
may provide for polymerization deeper into the HIPE foam. However,
if polymerization is done in an oxygen-containing environment,
there should be enough photoinitiator to initiate the
polymerization and overcome oxygen inhibition. Photoinitiators may
respond rapidly and efficiently to a light source with the
production of radicals, cations, and other species that are capable
of initiating a polymerization reaction. The photoinitiators used
in the present invention may absorb UV light at wavelengths of
about 200 nanometers (nm) to about 800 nm, in certain embodiments
about 200 nm to about 350 nm. If the photoinitiator is in the oil
phase, suitable types of oil-soluble photoinitiators include benzyl
ketals, .alpha.-hydroxyalkyl phenones, .alpha.-amino alkyl
phenones, and acylphospine oxides. Examples of photoinitiators
include 2,4,6-[trimethylbenzoyldiphosphine]oxide in combination
with 2-hydroxy-2-methyl-1-phenylpropan-1-one (50:50 blend of the
two is sold by Ciba Speciality Chemicals, Ludwigshafen, Germany as
DAROCUR.RTM. 4265); benzyl dimethyl ketal (sold by Ciba Geigy as
IRGACURE 651); .alpha.-,.alpha.-dimethoxy-.alpha.-hydroxy
acetophenone (sold by Ciba Speciality Chemicals as DAROCUR.RTM.
1173); 2-methyl-1-[4-(methyl thio)phenyl]-2-morpholino-propan-1-one
(sold by Ciba Speciality Chemicals as IRGACURE.RTM. 907);
1-hydroxycyclohexyl-phenyl ketone (sold by Ciba Speciality
Chemicals as IRGACURE.RTM. 184);
bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (sold by Ciba
Speciality Chemicals as IRGACURE 819); diethoxyacetophenone, and
4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-methylpropyl) ketone (sold
by Ciba Speciality Chemicals as IRGACURE.RTM. 2959); and
Oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone]
(sold by Lambeth spa, Gallarate, Italy as ESACURE.RTM. KIP EM.
The dispersed aqueous phase of a HIPE may have water, and may also
have one or more components, such as initiator, photoinitiator, or
electrolyte, wherein in certain embodiments, the one or more
components are at least partially water soluble.
One component of the aqueous phase may be a water-soluble
electrolyte. The water phase may contain from about 0.2% to about
40%, in certain embodiments from about 2% to about 20%, by weight
of the aqueous phase of a water-soluble electrolyte. The
electrolyte minimizes the tendency of monomers, comonomers, and
crosslinkers that are primarily oil soluble to also dissolve in the
aqueous phase. Examples of electrolytes include chlorides or
sulfates of alkaline earth metals such as calcium or magnesium and
chlorides or sulfates of alkali earth metals such as sodium. Such
electrolyte may include a buffering agent for the control of pH
during the polymerization, including such inorganic counterions as
phosphate, borate, and carbonate, and mixtures thereof. Water
soluble monomers may also be used in the aqueous phase, examples
being acrylic acid and vinyl acetate.
Another component that may be present in the aqueous phase is a
water-soluble free-radical initiator. The initiator may be present
at up to about 20 mole percent based on the total moles of
polymerizable monomers present in the oil phase. The initiator may
be present in an amount of from about 0.001 to about 10 mole
percent based on the total moles of polymerizable monomers in the
oil phase. Suitable initiators include ammonium persulfate, sodium
persulfate, potassium persulfate,
2,2'-azobis(N,N'-dimethyleneisobutyramidine)dihydrochloride, and
other suitable azo initiators. To reduce the potential for
premature polymerization which may clog the emulsification system,
addition of the initiator to the monomer phase may be just after or
near the end of emulsification.
Photoinitiators present in the aqueous phase may be at least
partially water soluble and may have between about 0.05% and about
10%, and in certain embodiments between about 0.2% and about 10% by
weight of the aqueous phase. Lower amounts of photoinitiator allow
light to better penetrate the HIPE foam, which may provide for
polymerization deeper into the HIPE foam. However, if
polymerization is done in an oxygen-containing environment, there
should be enough photoinitiator to initiate the polymerization and
overcome oxygen inhibition. Photoinitiators may respond rapidly and
efficiently to a light source with the production of radicals,
cations, and other species that are capable of initiating a
polymerization reaction. The photoinitiators used in the present
invention may absorb UV light at wavelengths of from about 200
nanometers (nm) to about 800 nm, in certain embodiments from about
200 nm to about 350 nm, and in certain embodiments from about 350
nm to about 450 nm. If the photoinitiator is in the aqueous phase,
suitable types of water-soluble photoinitiators include
benzophenones, benzils, and thioxanthones. Examples of
photoinitiators include
2,2'-Azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride;
2,2'-Azobis[2-(2-imidazolin-2-yl)propane]disulfate dehydrate;
2,2'-Azobis(1-imino-1-pyrrolidino-2-ethylpropane)dihydrochloride;
2,2'-Azobis[2-methyl-N-(2-hydroxyethyl)propionamide];
2,2'-Azobis(2-methylpropionamidine)dihydrochloride;
2,2'-dicarboxymethoxydibenzal acetone,
4,4'-dicarboxymethoxydibenzalacetone,
4,4'-dicarboxymethoxydibenzalcyclohexanone,
4-dimethylamino-4'-carboxymethoxydibenzalacetone; and
4,4'-disulphoxymethoxydibenzalacetone. Other suitable
photoinitiators that may be used in the present invention are
listed in U.S. Pat. No. 4,824,765 (Sperry et al.) issued Apr. 25,
1989.
In addition to the previously described components other components
may be included in either the aqueous or oil phase of a HIPE.
Examples include antioxidants, for example hindered phenolics,
hindered amine light stabilizers; plasticizers, for example dioctyl
phthalate, dinonyl sebacate; flame retardants, for example
halogenated hydrocarbons, phosphates, borates, inorganic salts such
as antimony trioxide or ammonium phosphate or magnesium hydroxide;
dyes and pigments; fluorescers; filler pieces, for example starch,
titanium dioxide, carbon black, or calcium carbonate; fibers; chain
transfer agents; odor absorbers, for example activated carbon
particulates; dissolved polymers; dissolved oligomers; and the
like.
The heterogeneous mass comprises enrobeable elements and discrete
pieces of foam. The enrobeable elements may be a web such as, for
example, nonwoven, a fibrous structure, an airlaid web, a wet laid
web, a high loft nonwoven, a needlepunched web, a hydroentangled
web, a fiber tow, a woven web, a knitted web, a flocked web, a
spunbond web, a layered spunbond/melt blown web, a carded fiber
web, a coform web of cellulose fiber and melt blown fibers, a
coform web of staple fibers and melt blown fibers, and layered webs
that are layered combinations thereof.
The enrobeable elements may be, for example, conventional absorbent
materials such as creped cellulose wadding, fluffed cellulose
fibers, wood pulp fibers also known as airfelt, and textile fibers.
The enrobeable elements may also be fibers such as, for example,
synthetic fibers, thermoplastic particulates or fibers,
tricomponent fibers, and bicomponent fibers such as, for example,
sheath/core fibers having the following polymer combinations:
polyethylene/polypropylene, polyethylvinyl acetate/polypropylene,
polyethylene/polyester, polypropylene/polyester,
copolyester/polyester, and the like. The enrobeable elements may be
any combination of the materials listed above and/or a plurality of
the materials listed above, alone or in combination.
The enrobeable elements may be hydrophobic or hydrophilic. The
enrobeable elements may be treated to be made hydrophobic. The
enrobeable elements may be treated to become hydrophilic.
The constituent fibers of the heterogeneous mass may be comprised
of polymers such as polyethylene, polypropylene, polyester, and
blends thereof. The fibers may be spunbound fibers. The fibers may
be meltblown fibers. The fibers may comprise cellulose, rayon,
cotton, or other natural materials or blends of polymer and natural
materials. The fibers may also comprise a super absorbent material
such as polyacrylate or any combination of suitable materials. The
fibers may be monocomponent, bicomponent, and/or biconstituent,
non-round (e.g., capillary channel fibers), and may have major
cross-sectional dimensions (e.g., diameter for round fibers)
ranging from 0.1-500 microns. The constituent fibers of the
nonwoven precursor web may also be a mixture of different fiber
types, differing in such features as chemistry (e.g. polyethylene
and polypropylene), components (mono- and bi-), denier (micro
denier and >20 denier), shape (i.e. capillary and round) and the
like. The constituent fibers may range from about 0.1 denier to
about 100 denier.
In one aspect, known absorbent web materials in an as-made may be
considered as being homogeneous throughout. Being homogeneous, the
fluid handling properties of the absorbent web material are not
location dependent, but are substantially uniform at any area of
the web. Homogeneity may be characterized by density, basis weight,
for example, such that the density or basis weight of any
particular part of the web is substantially the same as an average
density or basis weight for the web. By the apparatus and method of
the present invention, homogeneous fibrous absorbent web materials
are modified such that they are no longer homogeneous, but are
heterogeneous, such that the fluid handling properties of the web
material are location dependent. Therefore, for the heterogeneous
absorbent materials of the present invention, at discrete locations
the density or basis weight of the web may be substantially
different than the average density or basis weight for the web. The
heterogeneous nature of the absorbent web of the present invention
permits the negative aspects of either of permeability or
capillarity to be minimized by rendering discrete portions highly
permeable and other discrete portions to have high capillarity.
Likewise, the tradeoff between permeability and capillarity is
managed such that delivering relatively higher permeability may be
accomplished without a decrease in capillarity.
The heterogeneous mass may also include superabsorbent material
that imbibe fluids and form hydrogels. These materials are
typically capable of absorbing large quantities of body fluids and
retaining them under moderate pressures. The heterogeneous mass may
include such materials dispersed in a suitable carrier such as
cellulose fibers in the form of fluff or stiffened fibers.
The heterogeneous mass may include thermoplastic particulates or
fibers. The materials, and in particular thermoplastic fibers, may
be made from a variety of thermoplastic polymers including
polyolefins such as polyethylene (e.g., PULPEX.RTM.) and
polypropylene, polyesters, copolyesters, and copolymers of any of
the foregoing.
Depending upon the desired characteristics, suitable thermoplastic
materials include hydrophobic fibers that have been made
hydrophilic, such as surfactant-treated or silica-treated
thermoplastic fibers derived from, for example, polyolefins such as
polyethylene or polypropylene, polyacrylics, polyamides,
polystyrenes, and the like. The surface of the hydrophobic
thermoplastic fiber may be rendered hydrophilic by treatment with a
surfactant, such as a nonionic or anionic surfactant, e.g., by
spraying the fiber with a surfactant, by dipping the fiber into a
surfactant or by including the surfactant as part of the polymer
melt in producing the thermoplastic fiber. Upon melting and
resolidification, the surfactant will tend to remain at the
surfaces of the thermoplastic fiber. Suitable surfactants include
nonionic surfactants such as Brij 76 manufactured by ICI Americas,
Inc. of Wilmington, Del., and various surfactants sold under the
Pegosperse.RTM. trademark by Glyco Chemical, Inc. of Greenwich,
Conn. Besides nonionic surfactants, anionic surfactants may also be
used. These surfactants may be applied to the thermoplastic fibers
at levels of, for example, from about 0.2 to about 1 g. per sq. of
centimeter of thermoplastic fiber.
Suitable thermoplastic fibers may be made from a single polymer
(monocomponent fibers), or may be made from more than one polymer
(e.g., bicomponent fibers). The polymer comprising the sheath often
melts at a different, typically lower, temperature than the polymer
comprising the core. As a result, these bicomponent fibers provide
thermal bonding due to melting of the sheath polymer, while
retaining the desirable strength characteristics of the core
polymer.
Suitable bicomponent fibers for use in the present invention may
include sheath/core fibers having the following polymer
combinations: polyethylene/polypropylene, polyethylvinyl
acetate/polypropylene, polyethylene/polyester,
polypropylene/polyester, copolyester/polyester, and the like.
Particularly suitable bicomponent thermoplastic fibers for use
herein are those having a polypropylene or polyester core, and a
lower melting copolyester, polyethylvinyl acetate or polyethylene
sheath (e.g., DANAKLON.RTM., CELBOND.RTM. or CHISSO.RTM.
bicomponent fibers). These bicomponent fibers may be concentric or
eccentric. As used herein, the terms "concentric" and "eccentric"
refer to whether the sheath has a thickness that is even, or
uneven, through the cross-sectional area of the bicomponent fiber.
Eccentric bicomponent fibers may be desirable in providing more
compressive strength at lower fiber thicknesses. Suitable
bicomponent fibers for use herein may be either uncrimped (i.e.
unbent) or crimped (i.e. bent). Bicomponent fibers may be crimped
by typical textile means such as, for example, a stuffer box method
or the gear crimp method to achieve a predominantly two-dimensional
or "flat" crimp.
The length of bicomponent fibers may vary depending upon the
particular properties desired for the fibers and the web formation
process. Typically, in an airlaid web, these thermoplastic fibers
have a length from about 2 mm to about 12 mm long such as, for
example, from about 2.5 mm to about 7.5 mm long, and from about 3.0
mm to about 6.0 mm long. Nonwoven fibers may be between 5 mm long
and 75 mm long, such as, for example, 10 mm long, 15 mm long, 20 mm
long, 25 mm long, 30 mm long, 35 mm long, 40 mm long, 45 mm long,
50 mm long, 55 mm long, 60 mm long, 65 mm long, or 70 mm long. The
properties-of these thermoplastic fibers may also be adjusted by
varying the diameter (caliper) of the fibers. The diameter of these
thermoplastic fibers is typically defined in terms of either denier
(grams per 9000 meters) or decitex (grams per 10,000 meters).
Suitable bicomponent thermoplastic fibers as used in an airlaid
making machine may have a decitex in the range from about 1.0 to
about 20 such as, for example, from about 1.4 to about 10, and from
about 1.7 to about 7 decitex.
The compressive modulus of these thermoplastic materials, and
especially that of the thermoplastic fibers, may also be important.
The compressive modulus of thermoplastic fibers is affected not
only by their length and diameter, but also by the composition and
properties of the polymer or polymers from which they are made, the
shape and configuration of the fibers (e.g., concentric or
eccentric, crimped or uncrimped), and like factors. Differences in
the compressive modulus of these thermoplastic fibers may be used
to alter the properties, and especially the density
characteristics, of the respective thermally bonded fibrous
matrix.
The heterogeneous mass may also include synthetic fibers that
typically do not function as binder fibers but alter the mechanical
properties of the fibrous webs. Synthetic fibers include cellulose
acetate, polyvinyl fluoride, polyvinylidene chloride, acrylics
(such as Orlon), polyvinyl acetate, non-soluble polyvinyl alcohol,
polyethylene, polypropylene, polyamides (such as nylon),
polyesters, bicomponent fibers, tricomponent fibers, mixtures
thereof and the like. These might include, for example, polyester
fibers such as polyethylene terephthalate (e.g., DACRON.RTM. and
KODEL.RTM.), high melting crimped polyester fibers (e.g.,
KODEL.RTM. 431 made by Eastman Chemical Co.) hydrophilic nylon
(HYDROFIL.RTM.), and the like. Suitable fibers may also
hydrophilized hydrophobic fibers, such as surfactant-treated or
silica-treated thermoplastic fibers derived from, for example,
polyolefins such as polyethylene or polypropylene, polyacrylics,
polyamides, polystyrenes, polyurethanes and the like. In the case
of nonbonding thermoplastic fibers, their length may vary depending
upon the particular properties desired for these fibers. Typically
they have a length from about 0.3 to 7.5 cm, such as, for example
from about 0.9 to about 1.5 cm. Suitable nonbonding thermoplastic
fibers may have a decitex in the range of about 1.5 to about 35
decitex, such as, for example, from about 14 to about 20
decitex.
However structured, the total absorbent capacity of the
heterogeneous mass containing foam pieces should be compatible with
the design loading and the intended use of the mass. For example,
when used in an absorbent article, the size and absorbent capacity
of the heterogeneous mass may be varied to accommodate different
uses such as incontinence pads, pantiliners, regular sanitary
napkins, or overnight sanitary napkins. The heterogeneous mass may
also include other optional components sometimes used in absorbent
webs. For example, a reinforcing scrim may be positioned within the
respective layers, or between the respective layers, of the
heterogeneous mass.
The heterogeneous mass comprising open-cell foam pieces produced
from the present invention may be used as an absorbent core or a
portion of an absorbent core in absorbent articles, such as
feminine hygiene articles, for example pads, pantiliners, and
tampons; disposable diapers; incontinence articles, for example
pads, adult diapers; homecare articles, for example wipes, pads,
towels; and beauty care articles, for example pads, wipes, and skin
care articles, such as used for pore cleaning.
The heterogeneous mass may be used as an absorbent core for an
absorbent article. The absorbent core may be relatively thin, less
than about 5 mm in thickness, or less than about 3 mm, or less than
about 1 mm in thickness. Cores having a thickness of greater than 5
mm are also contemplated herein. Thickness may be determined by
measuring the thickness at the midpoint along the longitudinal
centerline of the absorbent structure by any means known in the art
for doing while under a uniform pressure of 0.25 psi. The absorbent
core may comprise absorbent gelling materials (AGM), including AGM
fibers, as is known in the art.
The heterogeneous mass may be formed or cut to a shape, the outer
edges of which define a periphery. Additionally, the heterogeneous
mass may be continuous such that it may be rolled or wound upon
itself, with or without the inclusion of preformed cut lines
demarcating the heterogeneous mass into preformed sections.
When used as an absorbent core, the shape of the heterogeneous mass
may be generally rectangular, circular, oval, elliptical, tapered
at one or both ends, hourglass, star, horseshoe, hearts, the like,
or combinations thereof. Absorbent core may be generally centered
with respect to the longitudinal centerline and transverse
centerline of an absorbent article. The profile of absorbent core
may be such that more absorbent is disposed near the center of the
absorbent article. For example, the absorbent core may be thicker
in the middle, and tapered at the edges in a variety of ways known
in the art.
The presence of a smooth transition zone provides continuity of
capillary suction and of fluid path, which are essential to proper
dewatering of the acquisition layer, re-establishing the suction
needed for further acquiring fluid from the topsheet layer.
Further, Applicants have found that by using a fibrous structure in
the acquisition portion of the absorbent structure intimately
connected to the topsheet on one surface of the acquisition portion
of the stratum and intimately connected to the storage portion of
the absorbent structure on the other surface of the acquisition
portion of the stratum allows for faster fluid acquisition, leading
to improved topsheet dryness after consecutive 0.5 ml gushes. For
example, the absorbent stratum, as shown in FIG. 3, exhibits a
topsheet residual moisture after the second 0.5 ml gush of
approximately 0.03 a.u. after 5 minutes, while in FIG. 2, the
structure exhibits a topsheet a.u. after the second 0.5 ml gush of
approximately 0.15 a.u after five minutes. As shown in FIG. 3, the
absorbent structure may exhibit a topsheet residual moisture after
a second 0.5 ml gush of approximately between 0.1 a.u. and 0.01
a.u., such as, for example, 0.09 a.u., 0.08 a.u., 0.07 a.u., 0.06
a.u., 0.05 a.u., 0.04 a.u., and 0.03 a.u. after 5 minutes.
This has been achieve through the creation of a heterogeneous mass
absorbent composite structure comprising an acquisition layer
comprised of enrobeable elements with very high permeability
(nonwoven substrate), a storage layer with very high capillary
suction (a high internal phase emulsion), and a transition zone
exhibited by the area where the enrobeable elements are fully
enrobed by the high internal phase emulsion foam.
The capillary suction is driven mostly by the high internal phase
emulsion foam layer with a progressive decrease in capillary
suction (bigger cells) as we move towards the top. The intrinsic
properties of the foam (average cell size and cell size
distribution, average window size and window size distribution,
porosity, caliper and surface treatment) are then gradually
transitioned to the intrinsic properties of the
substrate/acquisition layer through the presence of a transition
layer where the two are intimately intertwined.
Without being bound by theory, it is believed that this
construction significantly improves the fluid handling performance
of the system vs. having the substrate glued on top of a single
layer of HIPE foam by mean of two effects: 1) it increases the
speed of acquisition of the absorbent structure by providing a
capillary gradient the fluid would preferentially follow and 2) it
provides a better mean for dewatering the Topsheet, and restoring
the pre-gush saturation level in the nonwoven material thanks to
the fluid path continuity (i.e. the absence of a
discontinuity--aka, void--in the construction).
Specifically, without being bound by theory, it has been found that
a smooth transition zone
Demonstrating the superiority of such a construction requires a
very specific methodology capable of showing fluid partitioning
within an absorbent article and how far/close the fluid is to the
surface/consumer skin. This is covered in the section below
disclosing the NMR test method and the data shown in FIGS. 2 and
3.
The absorbent structure heterogeneous mass may serve as any portion
of an absorbent article. The absorbent structure heterogenous mass
may serve as the absorbent core of an absorbent article. A stratum
may serve as a portion of the absorbent core of an absorbent
article. More than one absorbent structure stratum may be combined
wherein each absorbent structure single stratum differs from at
least one other absorbent structure single stratum. The different
two or more absorbent structures stratums may be combined to form
an absorbent core. The absorbent article may further comprise a
topsheet and a backsheet.
The absorbent structure single stratum may be used as a topsheet
for an absorbent article. The absorbent structure single stratum
may be combined with an absorbent core or may only be combined with
a backsheet.
The absorbent structure single stratum may be combined with any
other type of absorbent layer such as, for example, a storage or
acquisition layer comprising a layer of cellulose, a layer
comprising superabsorbent gelling materials, a layer of absorbent
airlaid fibers, or a layer of absorbent foam. Other absorbent
layers not listed are contemplated herein.
The absorbent structure single stratum may be utilized by itself
for the absorption of fluids without placing it into an absorbent
article.
An absorbent article may comprise a liquid pervious topsheet. The
topsheet suitable for use herein may comprise wovens, non-wovens,
and/or three-dimensional webs of a liquid impermeable polymeric
film comprising liquid permeable apertures. The topsheet for use
herein may be a single layer or may have a multiplicity of layers.
For example, the wearer-facing and contacting surface may be
provided by a film material having apertures which are provided to
facilitate liquid transport from the wearer facing surface towards
the absorbent structure. Such liquid permeable, apertured films are
well known in the art. They provide a resilient three-dimensional
fibre-like structure. Such films have been disclosed in detail for
example in U.S. Pat. Nos. 3,929,135, 4,151,240, 4,319,868,
4,324,426, 4,343,314, 4,591,523, 4,609,518, 4,629,643, 4,695,422 or
WO 96/00548.
The absorbent articles of the absorbent structure may also comprise
a backsheet and a topsheet. The backsheet may be used to prevent
the fluids absorbed and contained in the absorbent structure from
wetting materials that contact the absorbent article such as
underpants, pants, pajamas, undergarments, and shirts or jackets,
thereby acting as a barrier to fluid transport. The backsheet may
also allow the transfer of at least water vapour, or both water
vapour and air through it.
Especially when the absorbent article finds utility as a sanitary
napkin or panty liner, the absorbent article may be also provided
with a panty fastening means, which provides means to attach the
article to an undergarment, for example a panty fastening adhesive
on the garment facing surface of the backsheet. Wings or side flaps
meant to fold around the crotch edge of an undergarment may be also
provided on the side edges of the napkin.
FIG. 1 is an SEM micrograph of a heterogeneous mass 22 after
formation means or the forming of canals. As shown in FIG. 1, the
absorbent stratum 40 is a heterogeneous mass 22 comprising a first
planar nonwoven 44 having a first surface 46 and a second surface
48 and a second planar nonwoven 50 having a first surface 52 and a
second surface 54. An open cell foam piece 25 enrobes a portion of
the first planar nonwoven 44 and a portion of the second planar
nonwoven 50. The planar nowovens are shown as wavy due to the
impact of the formation means.
As shown in FIG. 1, the enrobeable elements are highly porous and
designed to work as an acquisition layer for the absorbent core
while the non-integrated foam serves as a storage layer. This
allows creating capillary suction continuity and a capillary
suction gradient from top to bottom, which would drive the fluid
into the storage core layer (HIPE foam as shown).
FIGS. 2 and 3 show two plots of NMR profiles of signal (which
correlates linearly with moisture content) as function of position
within product respectively for a current marketed product (FIG. 2)
and the absorbent core of FIG. 1 (FIG. 3) using the same topsheet
as the marketed product.
As shown in FIGS. 2 and 3, as viewed from left to right, the first
(1) peak, consistent across the three samples is the double-side
tape placed to identify the beginning of a specimen. Starting with
the current market product in FIG. 2, we see a scan of the dry
sample (2), then a scan of the sample after the first 0.5 mL gush
(3) and then a scan of the sample after the second 0.5 mL gush (4).
Each scan is taken 5 min after gush.
As shown in FIG. 2, the first peak (5) in the scan is the fluid
distribution of the first 0.5 ml gush across the gradient
core/acquisition structure. There is a linear trend going from the
absorbent core (CORE) down the Secondary topsheet (STS) and
Topsheet (TS) which reflect the capillary suction gradient (i.e. at
equilibrium, the partitioning of fluid follows capillary
potentials, hence more fluid is stored by higher capillary suction
elements). Within the curve, we can identify that the majority of
the first 0.5 ml gush has entered the absorbent core, that the
interface (6a) between the absorbent core and the secondary top
sheet (gap) can be identified by the peak-valley transition, and
that another transition (7a) can be seen from Topsheet to the
secondary topsheet. Within the curve, we can identify that the
majority of the second 0.5 ml gush has also entered the absorbent
core, that the interface (6b) between the absorbent core and the
secondary top sheet (gap) can be identified by the peak-valley
transition, and that another transition (7b) can be seen from
Topsheet to the secondary topsheet. The topsheet remains wet after
the second gush (close to 0.15 a.u., or center of STS after first
gush). As shown in FIG. 2, in the positional range (4200 to 4500
microns) consistent with the TS, one can see an increase in the
slope or an inflection indicating an increase in fluid on the
topsheet between the acquisition scan of the first gush and the
acquisition scan of the second gush. As shown in FIG. 2, the
interface between any two layers is characterized by an inflection
point in the acquisition scan wherein the slope is greater than or
equal to zero. These inflection points are identified by 6a, 6b,
7a, and 7b.
Finally, viewing FIG. 3, one can see how the absorbent structure of
FIG. 1 shows a smooth transition zone. Specifically, as seen in
FIG. 3, one can see in scan (8) that the vast majority of the first
0.5 ml gush has entered the absorbent core, and very little fluid
is left on either the STS or the TS (not shown). The third scan (9)
of FIG. 3 represents the second 0.5 ml gush. As shown by the third
scan (9), the second 0.5 ml gush has also entered the absorbent
core and the interfaces between the acquisition portion and the
storage portion (10) of the stratum and between the acquisition
portion and the topsheet (11) both exhibit smooth transition zones
with slopes less than zero. As shown in FIG. 3, after the second
0.5 ml gush, the topsheet exhibits an a.u. of less than 0.03. For
reference, the absorbent stratum analyzed in FIG. 3 is a 27:1 oil
to water ratio HIPE extruded onto Fitesa 60 gsm AQL and then
polymerized. Once polymerized 30 gsm Spunlace is glued on the other
side. The core is Ring-Rolled (mechanically opened) to about 30%
width extension.
EXAMPLES
A. An absorbent product comprising a topsheet, a backsheet, and an
absorbent core, the absorbent core comprising an absorbent
structure comprising one or more stratum comprising one or more
enrobeable elements, wherein a smooth transition zone is exhibited
between an acquisition portion of the absorbent structure and a
storage portion of the absorbent structure. B. The absorbent
product according to paragraph A, wherein the enrobeable elements
comprise of nonwoven fibers having an average thickness, as
measured per SEM, ca. between 100 and 600 um. C. The absorbent
product according to paragraph A or B, wherein the smooth
transition zone comprises open-cell foam comprising pores having an
average diameter between 20 micron and 60 micron. D. The absorbent
according to paragraph C, wherein the smooth transition zone
comprises pores having an average diameter between 30 micron and 40
micron. E. The absorbent product according to any of paragraphs
A-D, wherein the smooth transition zone to caliper ratio is between
0.1 and 0.4. F. The absorbent product according to any of
paragraphs A-E, wherein the ratio of the Capillary Work Potential
of the topsheet to the Capillary Work Potential to the absorbent
structure is below 1.4. G. The absorbent product according to
paragraph C, wherein the ratio of the basis weight of the fibers to
the basis weight of the open-cell foam is below 0.48. H. The
absorbent product according to paragraph C, wherein the open-cell
foam comprises an average cell size above 20 micron and a basis
weight above 110 gsm. I. An absorbent product comprising a
topsheet, a backsheet, and an absorbent core, the absorbent core
comprising an absorbent structure comprising one or more stratum
comprising one or more enrobeable elements and open cell foam,
wherein a smooth transition zone is exhibited between an
acquisition portion of the absorbent structure and a storage
portion of the absorbent structure, wherein the smooth transition
zone is demonstrated by a negative slope by a NMR technique. J. The
absorbent product according to paragraph I, wherein the enrobeable
elements comprise of nonwoven fibers having an average thickness,
as measured per SEM, ca. between 100 and 600 um. K. The absorbent
product according to paragraph I or J, wherein the smooth
transition zone comprises pores having an average diameter between
20 micron and 60 micron. L. The absorbent product according to any
of paragraphs I-K, wherein the smooth transition zone comprises
pores having an average diameter between 30 micron and 40 micron.
M. The absorbent product according to any of paragraphs I-L,
wherein the smooth transition zone to caliper ratio is between 0.1
and 0.4. N. The absorbent product according to any of paragraphs
I-M, wherein the ratio of the Capillary Work Potential of the
topsheet to the Capillary Work Potential to the carrier is below
1.4. O. The absorbent product according to any of paragraphs I-N,
wherein the ratio of the basis weight of the carrier to the basis
weight of the foam is below 0.48. P. The absorbent product
according to any of paragraphs I-O, wherein the open-cell foam
comprises an average cell size above 20 micron and a basis weight
above 110 gsm. Q. An absorbent product comprising a topsheet, a
backsheet, and an absorbent core, the absorbent core comprising an
absorbent structure comprising one or more stratum comprising one
or more enrobeable elements and open cell foam, wherein a smooth
transition zone is exhibited between an acquisition portion of the
absorbent structure and a storage portion of the absorbent
structure, wherein the smooth transition zone is demonstrated by a
negative slope by a NMR technique, wherein the smooth transition
zone comprises of pores of average diameter between 20 micron and
60 micron. R. The absorbent product according to paragraph Q,
wherein the smooth transition zone comprises pores having an
average diameter between 30 micron and 40 micron. S. The absorbent
product according to paragraph Q or R, wherein the smooth
transition zone to caliper ratio is between 0.1 and 0.4. Kinetics
and 1D Liquid Distribution by NMR-MOUSE
The NMR-MOUSE (Mobile Universal Surface Explorer) is a portable
open NMR sensor equipped with a permanent magnet geometry that
generates a highly uniform gradient perpendicular to the scanner
surface (shown in FIGS. 6-7). A frame 1007 with horizontal plane
1006 supports the specimen and remains stationary during the test.
A flat sensitive volume of the specimen is excited and detected by
a surface rf coil 1012 placed on top of the magnet 1010 at a
position that defines the maximum penetration depth into the
specimen. By repositioning the sensitive slice across the specimen
by means of a high precision lift 1008, the scanner can produce
one-dimensional profiles of the specimen's structure with high
spatial resolution.
An exemplary instrument is the Profile NMR-MOUSE model PM25 with
High-Precision Lift available from Magritek Inc., San Diego, Calif.
Requirements for the NMR-MOUSE are a 100 .mu.m resolution in the
z-direction, a measuring frequency of 13.5 MHz, a maximum measuring
depth of 25 mm, a static gradient of 8 T/m, and a sensitive volume
(x-y dimension) of 40 by 40 mm.sup.2. Before the instrument can be
used, perform phasing adjustment, check resonance frequency and
check external noise level as per the manufacturer's instruction. A
syringe pump capable of delivering test fluid in the range of 1
mL/min to 5 mL/min.+-.0.01 mL/min is used to dose the specimen. All
measurements are conducted in a room controlled at 23.degree.
C..+-.0.5.degree. C. and 50%.+-.2% relative humidity.
Two test solutions are prepared. The first is 0.9% w/v saline
solution prepared as 9.0 g of NaCl diluted to 1 L deionized water.
The second is Paper Industry Fluid (PIF) prepared as 15 g
carboxymethylcellulose, 10 g NaCl, 4 g NaHCO.sub.3, 80 g glycerol
(all available from SigmaAldrich) in 1000 g distilled water. 2 mM/L
of Diethylenetriaminepentaacetic acid gadolinium (III) dihydrogen
salt (available from SigmaAldrich) is added to each. After addition
the solutions are stirred using an shaker at 160 rpm for one hour.
Afterwards the solutions are checked to assure no visible
undissolved crystals remain. The solution is prepared 10 hours
prior to use.
Products for testing are conditioned at 23.degree.
C..+-.0.5.degree. C. and 50%.+-.2% relative humidity for two hours
prior to testing. Identify the intersection of the lateral and
longitudinal center line of the product. Cut a 40.0 mm by 40.0 mm
specimen from the product, centered at that intersection, with the
cut edges parallel and perpendicular to the longitudinal axis of
the product. The garment facing side of the specimen 1003 is
mounted on a 50 mm.times.50 mm.times.0.30 mm glass slide 1001 using
a 40.0 mm by 40.0 mm piece of double-sided tape 1002 (tape must be
suitable to provide NMR Amplitude signal). A top cap 1004 is
prepared by adhering two 50 mm.times.50 mm.times.0.30 mm glass
slides 1001 together using a 40 mm by 40 mm piece of two-sided tape
1002. The cap is then placed on top of the specimen. The two tape
layers are used as functional markers to define the dimension of
the specimen by the instrument.
First a 1-D Dry Distribution Profile of the specimen is collected.
Place the prepared specimen onto the instrument aligned over top
the coils. Program the NMR-MOUSE for a Carr-Purcell-Meiboom-Gill
(CPMG) pulse sequence consisting of a 90.degree. x-pulse follow by
a refocusing pulse of 180.degree. y-pulse using the following
conditions:
Repetition Time=500 ms
Number of Scans=8
Number of Echoes=8
Resolution=100 .mu.m
Step Size=-100 .mu.m
Collect NMR Amplitude data (in arbitrary units, a.u.) versus depth
(.mu.m) as the high precision lift steps through the specimen's
depth. A representative graph is shown in FIG. 4A.
The second measure is the Kinetic Experiment of the test fluid
moving though the sensitive NMR volume as test fluid is slowly
added to the top of the specimen. The "trickle" dose is followed by
a "gush" dose added using a calibrated dispenser pipet. Program the
NMR-MOUSE for a CPMG pulse sequence using the following
conditions:
Measurement Depth=5 mm
Repetition Time=200 ms
90.degree. Amplitude=-7 dB
180.degree. Amplitude=0 dB
Pulse Length=5 .mu.s Echo Time=90 .mu.s
Number of Echoes=128
Echo Shift=1 .mu.s
Experiments before trigger=50
Experiments after trigger=2000
Rx Gain=31 dB
Acquisition Time=8 .mu.s
Number of Scans=1
Rx Phase is determined during the phase adjustment as described by
the vendor. A value of 230.degree. was typical for our experiments.
Pulse length depends on measurement depth which here is 5 mm. If
necessary the depth can be adjusted using the spacer 1011.
Using the precision lift adjust the height of the specimen so that
the desired target region is aligned with the instruments sensitive
volume. Target regions can be chosen based on SEM cross sections.
Program the syringe pump to deliver 1.00 mL/min.+-.0.01 mL for 1.00
min for PIF test fluid or 5.00 mL/min.+-.0.01 mL for 1.00 min for
0.9% Saline test fluid. Start the measurement and collect NMR
Amplitude (a.u.) for 50 experiments before initiating fluid flow to
provide a signal baseline. Position the outlet tube from the
syringe pump over the center of the specimen and move during
applying liquid over the total sample surface, but do not touch the
borders of the sample. Trigger the system to continue collection of
NMR amplitude data while simultaneously initiating fluid flow for 1
mL over 60 sec. At 300 sec after the trigger, add 0.50 mL of test
fluid at approximately 0.5 mL/sec to the center of the specimen via
a calibrated Eppendorf pipet. A representative example of the NMR
Amplitude versus time graph is shown in FIG. 5.
The third measurement is a 1-D Wet Distribution Profile Immediately
after the Kinetic measurement is complete, replace the cap on the
specimen. The Wet Distribution is run under the same experimental
conditions as the previous Dry Distribution, described above. A
representative graph is shown in FIG. 4B.
Calibration of the NMR Amplitude for the Kinetic signal can be
performed by filling glass vials (8 mm outer diameter and a defined
inner diameter by at least 50 mm tall) with the appropriate fluid.
Set the instrument conditions as described for the kinetics
experiment. A calibration curve is constructed by placing an
increasing number of vials onto the instrument (vials should be
distributed equally over the 40 mm.times.40 mm measurement region)
and perform the kinetic measurements. The volumes are calculated as
the summed cross sectional area of the vials present multiplied by
the z-resolution where Resolution (mm) is calculated as
1/Acquisition Time (s) divided by the instruments Gradient Strength
(Hz/mm) The Calibration of the NMR Amplitude for the Distribution
Profile is performed as an internal calibration based on the dry
and wet profiles. In this procedure the area beneath wet and dry
profile were calculated and after subtracting them the total area
(excluding markers) was obtained. This total area is correlated to
the amount of applied liquid (here 1.5 mL). The liquid amount
(.mu.L) per 100 .mu.m step can then be calculated.
The dimensions and values disclosed herein are not to be understood
as being strictly limited to the exact numerical values recited.
Instead, unless otherwise specified, each such dimension is
intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm."
Values disclosed herein as ends of ranges are not to be understood
as being strictly limited to the exact numerical values recited.
Instead, unless otherwise specified, each numerical range is
intended to mean both the recited values and any integers within
the range. For example, a range disclosed as "1 to 10" is intended
to mean "1, 2, 3, 4, 5, 6, 7, 8, 9, and 10."
All documents cited in the Detailed Description of the Invention
are, in relevant part, incorporated herein by reference; the
citation of any document is not to be construed as an admission
that it is prior art with respect to the present invention. To the
extent that any meaning or definition of a term in this document
conflicts with any meaning or definition of the same term in a
document incorporated by reference, the meaning or definition
assigned to that term in this document shall govern.
While particular embodiments of the present invention have been
illustrated and described, it would be obvious to those skilled in
the art that various other changes and modifications can be made
without departing from the spirit and scope of the invention. It is
therefore intended to cover in the appended claims all such changes
and modifications that are within the scope of this invention.
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